Effect Of Annealing Process On Microstructure And Properties Of Micro-carbon Deep Drawing Duplex Steel

With the improvement of people’s quality of life,the increasing awareness of environmental protection,and the promotion of energy-saving and emission reduction policies,automotive lightweighting has become the focus of the automotive industry.Traditional automotive structural materials are gradually replaced by advanced high-strength steels and other materials.As one of the more mature advanced high-strength steels,duplex steel has high strength,good elongation and high initial work hardening rate,and is usually used for automotive wheel rims,collision strengthening frames and suspension parts,etc.The reason why duplex steel is less used for automotive coverings is its low deep punching property.In this paper,two test steels with different compositions,Cu-Ni and Al-Mo steels,were designed to study different annealing processes,weave evolution,strain hardening mechanisms and numerical simulations of stamping and forming for related analysis,and the main conclusions are as follows.（1）Simulation analysis of the test steels based on Jmat Pro thermodynamic software.Ac₁of Cu-Ni test steel was 702°C and Ac₃temperature was 880°C.The continuous cooling transition curve analysis,only when the cooling rate is greater than 10°C/s,the pearlite in the organization at room temperature disappears.In order to get the right amount of martensite and improve the deep-drawing performance of the test steel,the cooling rate was set to 50℃/s.The temperature of Ac₁for Al-Mo test steel was 674℃,and the temperature of Ac₃was 936℃.The higher the annealing temperature,the greater the cooling rate required to obtain martensite,in order to ensure a certain amount of martensite,the cooling rate is set to 50℃/s.（2）Study the effect of annealing process on the microstructure mechanical properties of the test steels.The data show that:both test steels increase in tensile strength with increasing annealing temperature,and deep impulse is taken as the maximum value at720°C-820°C annealing process,with the maximum r value of 1.24 for Cu-Ni test steel and1.36 for Al-Mo test steel.deep impulse of the test steel is better than that of the non-stage annealing process under the staged annealing process,mainly because the recrystallization stage promotes{111}The development of the weave structure improves the deep punching properties of the test steels.（3）According to the analysis of uniaxial tensile phase microstructure change state based on transient work hardening rate,Hollomom and modified C-J equation,for Cu-Ni test steel uniform tensile process appears in two phases,due to less martensite tissue,the first phase is a small amount of hard phase tissue and ferrite synergistic plastic deformation,the second phase rapid fracture;for Al-Mo test steel,martensite volume fraction more,the homogeneous tensile phase is divided into three stages,the first stage,two phase plastic incompatibility,the reverse stress in ferrite rapidly increasing;the second stage,the mutual control of reverse stress and martensite interface;the third stage,dislocation cell formation,dynamic recovery,cross-slip in ferrite and yield fracture of martensite particles.（4）The test steel was simulated numerically with the software Dynaform for the press formability of the automotive wing panel,and the forming limit diagram,thickness thinning rate and strain distribution diagram of the test steel were analyzed.The Al-Mo test steel had higher formability r value and better forming results,while the Cu-Ni test steel showed severe fracture at the early edge of the press.